California Black Oak (Quercus kelloggii)

Black oak leafblack oak, Kellogg oak

This information was originally published in Hardwoods of the Pacific Northwest, S.S. Niemiec, G.R. Ahrens, S. Willits, and D.E. Hibbs. 1995. Research Contribution 8. Oregon State University, Forest Research Laboratory

General Characteristics

California black oak is a deciduous member of the beech family (Fagaceae). It is the most abundant oak on the West Coast and is most similar in form and wood quality to eastern red oaks.

RangeSize, Longevity, and Form
Mature California black oaks (>90 years old) attain heights of 50 to 110 ft (130 ft maximum) and diameters of 14 to 40 in. (108 in. maximum), and may live 500 years. In closed stands on good sites, California black oaks develop narrow, thin crowns on straight, clear boles. Open-grown trees have broad crowns with multiple stems that fork repeatedly. A scrubby form of California black oak is common on marginal sites. The root system is usually composed of a surface root system and several deep vertical roots, which may spread laterally over bedrock; some roots penetrate cracks in the rock. Seedlings have a tap root.

Geographic Range
The native range of California black oak extends from Eugene, Oregon (lat 44°N), to the San Pedro de Martin Mountains of Baja California (lat 32°N). It grows in the valleys of southwestern Oregon and is abundant on the west side of the Sierra Nevada and in the northern and central Coast Range of California.

Timber Inventory
Among hardwoods on the West Coast, the inventory of California black oak (2662 MMCF) is second only to that of red alder. In the Pacific Northwest, it is restricted to southwestern Oregon, with a total volume of 131 MMCF (Appendix 1, Table 1).

Biology and Management

Tolerance, Crown Position
California black oak is intolerant of shade for most of its life. Young seedlings can persist in the shade; saplings can survive as intermediate trees, growing tall and thin towards the light. California black oak will grow towards openings, leaning as much as 15 to 20 degrees. Older trees cannot survive continued overtopping.

Ecological Role
California black oak may function as a climax species in transitional environments between conifer forest and chaparral. Over much of the range, it is probably a persistent subclimax species maintained by resprouts after periodic fire. On better sites in the absence of disturbance, California black oak is eventually replaced by more shade-tolerant or competitive associates (tanoak, Douglas-fir, California white fir, pines). Under harsh conditions, conifer regeneration is often restricted to sheltered areas under black oak; the black oak serve as nurse trees.

Although fire kills trees of all ages, periodic fires probably have maintained California black oak populations in many areas. Populations appear to be declining after decades of fire suppression. Prescribed burns of moderate to low intensity are recommended to improve regeneration of California black oak from seed.

Associated Vegetation
California black oak is the dominant tree over large areas classified as the black oak forest type, and it is a major component in other forest types dominated by conifers. The most common tree species associated with California black oak are ponderosa pine, Douglas-fir, tanoak, Pacific madrone, and Oregon white oak. Common shrub associates include greenleaf manzanita, whiteleaf manzanita, deerbrush, bear-clover, oceanspray, and poison-oak. Understory vegetation is generally sparse under California black oak, although shrubs may become abundant and competitive after fire or cutting.

Suitability and Productivity of Sites
To evaluate site productivity for California black oak, site index should be estimated where possible, using methods described by Powers (1972). In general, good ponderosa pine sites in the range of California black oak are also good black oak sites. The presence of tanoak with California black oak is also an indicator of good productivity for black oak. Early growth of stump sprouts is often independent of site quality; thus, older trees should be used to assess productivity.

California black oak is adapted to a climate characterized by hot, dry summers and cool, moist winters. Its climate has an average annual precipitation range of 30 to 70 in., with extremes of 12 to 110 in. Less than 5 percent of this moisture falls from June to September. California black oak grows best in a zone where 10 to 50 percent of the precipitation occurs as snow. Mean daily temperatures in this climate range from a minimum of 31 to 46 °F in January to a maximum of 66 to 82 °F in July.

California black oak has a high tolerance to drought. Deep roots help it avoid drought; it also withstands high levels of moisture stress. Black oak leaves are injured by extreme heat after cool, wet weather. Planted seedlings are susceptible to dieback from late spring frosts. Branches and boles may break from heavy snow or ice, particularly at forks. Sound, healthy trees are windfirm.

In Oregon, California black oak is found at elevations of 450 to 3000 ft. In California, it is most abundant at elevations of 1000 to 6000 ft in the north and 4000 to 7800 ft in the south. It is often restricted to north aspects at low elevations, and south to west aspects at high elevations. At middle elevations, it is found on all aspects.

California black oak grows best on deep, well-drained soils of medium to coarse texture. It is found on soils from a wide variety of parent materials across a wide range of textures. California black oak is often found on shallow, rocky soils, although its growth and form are poor. It seldom grows on clay soils, particularly clay topsoils. It does not tolerate poor drainage or flooding. California black oak may prefer relatively high levels of soil nutrients; fertilization greatly stimulates growth of seedlings in the wild.

Flowering & Fruiting
California black oak starts to produce seed as early as 30 years of age, but does not usually produce heavily before age 80. It flowers in spring, from mid-March to mid-May, depending on the environment. Separate male and female flowers are borne on the same plant. The greenish-red male flowers arise from leaf axils of the previous year, forming hairy aments 1.4 to 3.0 in. long. Female flowers emerge from leaf axils of the current year.

California black oak acorns mature during the second summer after pollination. The acorns are 0.7 to 1.7 in. long and 0.4 to 1.5 in. wide, and number from 52 to 147/lb. Acorns should be collected from late September to early November. The first acorns that fall (mid-August to mid-September) are usually infested with insects. Acorns should be collected soon after they fall to reduce losses in viability from extreme temperatures and losses to animals.

California black oak acorns require after-ripening and should either be planted immediately or stored under cool, moist conditions (33 to 34 °F) until spring planting. Germination capacity is quite variable, ranging from 21 to 95 percent; average rates were 31 to 38 percent in one large-scale test.

Regeneration from Seed
Natural regeneration from seed is uncertain and poorly distributed. Establishment of seedlings is most frequent under parent trees. Animals transport many seeds and facilitate the occasional establishment of seedlings away from the parent tree. Seedlings establish best on undisturbed litter or loose, well-aerated mineral soil. California black oak does not usually colonize compacted or heavy clay surface soils. Seedlings rapidly develop deep taproots (to 30 in.) the first year; shoot growth remains slow for the first 6 or more years.

Regeneration from Vegetative Sprouts
Most regeneration of California black oak results from basal sprouts, which are profuse after cutting or burning. Larger parent trees produce more abundant and more vigorous sprouts than do smaller trees. Sprout development is best in completely open conditions; shelterwood cuttings are not recommended for regenerating black oak sprouts. Stumps should be cut low to the ground in order to produce more vigorous, well-formed sprouts.

Regeneration from Planting
The performance of California black oak planted on several sites in California indicates fair potential for regenerating black oak in plantations. Fertilization greatly enhances growth of planted trees. Drought and pocket gophers are the most common causes of mortality. Late spring frost causes top dieback; injured seedlings typically resprout.

Site Preparation and Vegetative Management
Little site preparation is necessary for establishing stands from sprouts. Regeneration and growth may be enhanced by burning or mechanically removing slash that shades stumps.

On California black oak sites, shrubs are often sparse and not competitive. If vegetative competition is significant on a site, however, vegetation management will benefit California black oak sprouts or seedlings. Seedlings are most vulnerable to competition. Site preparation and later control of competing vegetation may accelerate the typically long transition stage from seedling to sapling.

Stand Management
California black oak sprouts initiate at high densities, after which self-thinning and expression of dominance proceed rapidly. Thinning young sprout clumps after 4 years is probably not beneficial. Thinning in older stands can improve diameter growth (up to 2 times) while favoring better quality trees. Results of one thinning study indicate that optimum stand and tree growth may be maintained at stand densities of 100 to 125 ft2 per acre. Thinning can increase the size and quality of epicormic branches. Density management strategies must be designed to minimize the impact of epicormic branches on wood quality. California black oak is best managed in even-aged stands or patches.

Mixed-species Stands
Top light must be maintained for good growth of California black oak in mixed stands. On good sites, associated tanoak and conifers may need to be controlled to maintain California black oak in the long term. Black oak may be used as a nurse tree to facilitate survival of conifer regeneration on low-elevation sites. Black oak is resistant to the annosus root rot (Heterobasidion annosum), which suggests a strategy of planting black oak in root-rot areas within conifer stands.

Growth and Yield
Seedlings grow slowly, reaching heights of 4 to 6 in. the first year, and often have slower shoot growth for 5 or more years while roots establish. Sprout growth averages about 2 ft per year for the first 10 years. Site index (50-year base) ranges from 30 to 70 ft, with an average of 50 ft. In natural stands, average diameter increment is about 1.8 in. per decade during the first 60 years, slowing to about 1.5 in. per decade by age 110.

California black oak stands in California average about 1213 ft3 per acre, with maximum volumes of 4000 ft3 per acre over 5 acres. One fully stocked stand of 70-year-old black oak had a volume of 5845 ft3 per acre with an average diameter of 12 in. and height of 62 ft.

Interactions with Wildlife
California black oak acorns are an important food source for birds, rodents, deer, and bear. Fluctuations in deer populations are sometimes correlated with the acorn crop. Large, hollow trees are common and provide habitat for cavity-nesting animals. Foliage is browsed by deer and elk.

Insects and Diseases
Many species of insects live on California black oak, but they seldom have significant impact. The carpenter worm (Prionoxystus robinae) damages the wood of black oak; other insects causing damage include the pit scales (Asterolecanium minus and A. quericola), the Pacific oak twig girdler (Agrilus angelicus), the California oakworm (Phryganidia californica), and the fruit-tree leafroller (Archips argyrospila).

Heart rots (Inonotus dryophilus and Laetiporus sulphureus) cause significant damage in old trees and in trees injured by logging, fire, or weather. The shoestring root rot, Armillaria ostoyae (A. mellea) commonly attacks older trees. Black oak is resistant to the annosus root rot (Heterobasidion annosum), which kills many other species.

California black oak hybridizes with Q. agrifolia (known as Quercus x ganderi) and with Q. wislizenii (known as Quercus x moreha). The latter hybrid is most common and has sparse evergreen foliage.

Harvesting and Utilization

Cruising and Harvesting
Diameter at breast height and total height can be used with tables or equations to estimate total tree volume in cubic feet and sawlog volume. California black oak trees have a tendency to split and “barberchair” during felling so care must be taken in making the undercut and leaving holding wood.

Logs are generally weighed or sold by the truckload, and conversion factors are used to convert back into board foot volumes. The logs check easily during storage and should be end-coated to prevent splits in the lumber. Log grades have also been used to effectively separate logs of different product quality and are recommended for marketing.

Product Recovery
Sawlogs usually have a minimum small-end diameter of 10 in. Smaller logs are chipped for pulp. Stain, discoloration, and end- and surface-checking are common problems with California black oak lumber if it is not processed within a short time after it is removed from the woods. One study found that 72 percent of the board-foot-scale was recovered as lumber; another study found that 60 percent of the weight is recovered as lumber products, 20 percent as slabs and edgings, and 20 percent as sawdust and shavings. The percentage of loss associated with edgings may be reduced if care is taken to prevent “over-edging” in the mill. Recovery of higher grade lumber from California black oak appears to be somewhat low compared to other hardwood species (Appendix 1, Table 2).

Wood Properties

The heartwood is light brown with pink to pale reddish-brown color; the sapwood is a pale yellowish-white to brownish-white. California black oak is a ring-porous wood, with earlywood pores that are large and distinct and form a conspicuous band with each growth ring. The latewood pores are small and numerous, and require a hand lens to view. The large earlywood vessels are almost always occluded by tyloses. Among the red oaks, California black oak has one of the lowest percentages of summer wood; for an oak, then, the wood is fairly fine-grained. The rays are numerous, short in height, and wide. When the wood is dry, it has no characteristic odor or taste. Distinctive burls are sometimes present. California black oak is commercially classed as a red oak in USDA Forest Service nomenclature.

California black oak weighs about 66 lb/ft3 when green and 40 lb/ft3 at 12 percent moisture content (MC). The average specific gravity is 0.51 (green) or 0.58 (ovendry).

Mechanical Properties
Because of its lower specific gravity and lower percentages of summer wood, California black oak has lower clear-specimen strength values than many of the eastern red oaks. It still is an oak, however, and possesses many desirable strength properties, including parallel and perpendicular compression resistance, and side hardness. It is suitable for most furniture design applications, and the lower grades perform well as pallet stock. It holds nails well, but will split unless it is prebored or pneumatic nailers are used. See Appendix 1, Table 3 for average mechanical properties for small, clear specimens.

Drying and Shrinkage
California black oak requires special care and attention to detail during an extended kiln schedule to properly reduce MC to a level suitable for interior products such as flooring, furniture, or millwork. Drying defects can cause serious downgrade; end- and surface-checking result from uncontrolled or overly rapid drying; honeycomb, collapse, and ring failure occur from wetwood; iron stains form when tannins contact certain metals; and grey sapwood staining will result if there is poor air circulation. Additionally, the wood can be inhabited by bacteria, which will complicate drying but will not affect the quality of the final dry product. The green MC of California black oak averages 105 percent (ovendry basis). Shrinkage values for green to ovendry (based on the original green size) are low, and average 3.6 percent radially and 6.6 percent tangentially. It is suggested that all the upper grades be air-dried to 20 percent MC and then kiln-dried according to a time schedule (See table below for the appropriate kiln schedule).

Black oak kiln schedule

The machining characteristics of California black oak are excellent. Because of its moderate specific gravity and tight grain, the feed speeds of machines can be greater for California black oak than for most of the other oaks, but still produce quality surfaces when planing, shaping, turning, boring, and sanding. The wood can be successfully bent when it is properly steamed and bending forms are utilized.

California black oak bonds satisfactorily and there are no unusual problems when gluing conditions are well controlled. Careful curing/ drying of glue joints is required to prevent sunken gluelines from subsequent machining.

California black oak finishes well, although it may be necessary to fill the grain to obtain a smooth finish. The heartwood/sapwood color variation can present difficulties if uniform color is desired. Dyes and transparent stains are better than heavily pigmented stains, which require the removal of any excess pigment from the wood.

The heartwood of California black oak is basically nondurable when exposed to conditions that are favorable to wood decay organisms. Iron staining will occur if ferrous products contact wet wood. Oxidative staining can additionally degrade improperly handled logs and lumber.

Black oak has been successfully peeled into veneer and used in cabinet fronts. It is used for moulding, millwork, paneling, furniture, flooring, veneer, edge-glued panels, pallets, chips for landscaping, and firewood.

Related Literature

HALL, G., and R. ALLEN. 1981. Wood products from California oaks, Cal Oak Lumber Company style. P. 362-368 in: Proceedings of the Symposium on the Ecology, Management, and Utilization of California Oaks. T.R. Plumb, tech. coord. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. General Technical Report PSW-44.

KAUFFMAN, J.B., and R.E. MARTIN. 1987. Effects of fire and fire suppression on mortality and mode of reproduction of California black oak (Quercus kelloggii Newb.). P. 122-126 in Proceedings of the Symposium on Multiple-Use Management of California’s Hardwood Resources.

T.R. Plumb and N.H. Pillsbury, tech. coords. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. General Technical Report PSW-100.

KOENIG, W.D., R.L. MUMME, W.J. CARMEN, and M.T. STANBACK. 1994. Acorn production by oaks in central coastal California: variation within and among years. Ecology 75:99-109.

MALCOLM, F.B. 1962. California black oak - a utilization study. USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin. Report No. 2237. 10 p.

McDONALD, P.M. 1969. Silvical characteristics of California black oak (Quercus kelloggii Newb.) USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. PSW-53.

McDONALD, P.M. 1983. Local volume tables for Pacific madrone, tanoak, and California black oak in north-central California. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. Research Note PSW-362. 6 p.

McDONALD, P.M. 1990. California black oak. P. 661-671 in Silvics of North America. Volume 2, Hardwoods. R.M. Burns and B.H. Honkala, coords. USDA Forest Service, Washington D.C. Agriculture Handbook 654.

McDONALD, P.M., D. MINORE, and T. ATZET. 1983. Southwestern Oregon-northern California hardwoods. P. 29-32 in Silvicultural Systems for the Major Forest Types of the United States. R. Burns, tech. compil. USDA Forest Service, Washington, D.C. Agriculture Handbook 445.

PLUMB, T.R., and P.M. McDonald. 1981. Oak management in California. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. General Technical Report PSW-54. 11 p.

POWELL, C. 1978. The California black oak: from saddle-soaped leather to pumpkin orange. Environment Southwest 481:3-50.

POWERS, R.F. 1972. Site index curves for unmanaged stands of California black oak. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. Research Note PSW 262. 5 p.

QUARLES, S.L. 1992. Acoustic emission associated with oak during drying. Wood and Fiber Science 24:2-12.